HP Freezer Before its repair, prior to every hpf run the instrument is subjected to a pretest to ensure that pressure maintenance, cooling time, and temperature maintenance meet the specifications required for an optimum freeze. Two-Photon: Aligning scan head. Measure point spread function (PSF) and general system development. SEM: Tested the resolution of S-900. Tested the emission and the signal to noise ratio. Tested the stability of the emission source.